1. Field of the Invention
The present invention relates to a storage system and storage system data migration method.
2. Description of the Related Art
A storage system, for example, is constituted by arranging a large number of disk drives in an array, and provides storage areas based on RAID (Redundant Array of Independent Disks). Logical volumes (Logical Units), which are logical storage areas, are formed on the physical storage area of each disk drive. A server, mainframe or other such host device can access a desired volume to read and write data by issuing a prescribed command to the storage system.
In accordance with operating a storage system, huge amounts of data come to be stored in the storage system. Accordingly, in order to effectively utilize the storage resources of a storage system, for example, so-called data migration technology has been proposed, whereby infrequently used data is stored on a low-speed disk drive.
One data migration technique generates respective disk pools for each type of disk drive, and presets various storage classes in the logical volumes inside the disk pools. Then, a file is moved to a logical volume having the optimum storage class based on the file's static and dynamic characteristics (Japanese Laid-open Patent No. 2004-295457).
Another data migration technique selects a volume, which satisfies preset reliability and performance conditions, and controls migration destinations in file units (Japanese Laid-open Patent No. 2004-70403).
In the prior art disclosed in the above-mentioned literature, data migration can be carried out in file units on the basis of file characteristics. However, even though files might have the same characteristics, their respective generation dates will differ, meaning the expiration dates of the respective files will vary.
For example, storage terms are established for respective types of data, such as e-mail data, invoice data, sales data, client data, and resident data, but the generation date of each file will differ, respectively. Therefore, even though files might be of the same type, their respective storage term expiration dates will differ. However, data migration, which takes such differences in file storage terms into consideration, is not addressed in the prior art. For this reason, in the prior art, even files of the same type, which were generated at times relatively close to one another, wind up being stored in different volumes, thereby reducing usability.
Further, there are cases in which the storage period required by type of file is longer than the life of the storage device. It is also quite possible that if a file is stored as-is in an obsolete storage device, this file will become difficult to read. Therefore, for example, thought is being given to migrating files from obsolete storage devices to tape devices for long-term storage. However, once a file has been migrated to a tape device, usability declines because it is no longer easy to access this file when file access is requested.